Neisseria meningitidis is a Gram-negative bacterium and the causative agent of meningococcal meningitis and septicemia. Its only known host is the human, and it may be carried asymptomatically by approximately 10% of the population (Caugant, D. et al, 1994, Journal of Clinical Microbiology, 32:323-30).
N. meningitidis may express a polysaccharide capsule, and this allows classification of the bacteria according to the nature of the capsule expressed. There are at least thirteen serogroups of N. meningitidis: A, B, C, 29-E, H, I, K, L, W135, X, Y and Z, of which serogroups A, B, and C cause 90% of meningococcal disease (Poolman, J. T. et al, 1995, Infectious Agents and Disease, 4:13-28). Vaccines directed against serogroups A and C are available, but the serogroup B capsular polysaccharide is poorly immunogenic and does not induce protection in humans.
Other membrane and extracellular components are therefore being examined for their suitability for inclusion in vaccines. Examples include the outer membrane proteins of classes 1, 2 and 3 (porins), and classes 4 (Rmp) and 5 (Opacity proteins). However, to date, none of these candidates is able to induce complete protection, particularly in children (Romero, J. D., 1994, Clinical Microbiology Review, 7:559-575; Poolman, J. T. et al, 1995, supra) .
To create an effective vaccine, it is necessary to identify components of N. meningitidis which are present in a majority of strains, and which are capable of inducing a protective immune response (bactericidal antibodies). In this regard, reference may be made to Brodeur et al. (International Publication WO 96/29412) who disclose a 22 kDa surface protein which is highly conserved across 99% of all known strains of N. meningitidis. Injection of purified recombinant 22-kDa surface protein protected 80% of immunized mice against development of a lethal infection by N. meningitidis. Notwithstanding the discovery of this protein, there is still a need to isolate more surface proteins of N. meningitidis which are highly conserved across a plurality of strains, and which have immuno-protective profiles against N. meningitidis, and/or which may be used in combination with other components of N. meningitidis to enhance the efficacy of protection against this organism.